The correction of eye glass lenses depends on the refractive index and the curvatures of both surfaces of the lens but when the degree of myodia or hypermetropia advances, the thickness of the lens for correcting it increases at the outer edge portion or the center portion and hence the appearance is spoiled and the lens becomes heavy in weight to give unpleasant feeling to the user. This problem can be improved by increasing the refractive index of glass material. However, if the refractive index of the glass increases, the specific gravity of the glass generally tends to increase. Therefore, a glass having a high refractive index and a low specific gravity has been demanded and such a glass is disclosed in, for example, Japanese Patent Publication No. 51141/81 and Japanese Patent Application (OPI) No. 126549/80. However, the glass disclosed therein contains a large amount of TiO.sub.2 to obtain a low specific gravity and, as a result, has a small Abbe number.
Therefore, the glass has the disadvantage that the chromatic aberration at the outer edge portion thereof is large when the glass is used as an eye glass lens. In particular, when the glass is used as an eye glass lens having a high diopter value, the chromatic aberration becomes a serious problem.
For the above reasons, a light weight glass having a high refractive index and simultaneously a large Abbe number is demanded.